Reloading...correct dram?

Q. i have a mec jr. 1 1/8 ounce slide bar. i also have lymans reloading book. i have been looking at the dram equivalent and it is a bit confusing. for some reason i am not understanding the link between shot weight and powder. everything i read is based on velocity. does it matter the weight of the shot if the proper velocity is reached? i guess that is where the dram threw me off. i know that a dram of 3 at 1 1/ z is different than a dram of 3 1/4 at 1 1/ z in terms of velocity. in the lyman reloading book they reference about six different types of shots loads in each category with only one velocity for all eight. should this be the reference i use? i can look up the powder, the grains, the velocity, the wad, and even the hull, i guess i am getting confused on how the different shot sizes affect each shot or if the ballistics says velocity can be the same with different shots. how woudl i know how to get the correct dram ? i am new to the reloading scene if you can't tell, but i want to make sure i am doing things right. when i first got started the guys at the sporting good stores were not that helpful. they pretty much told me this would work and this would work. thanks for your help.

A. First get a Hodgdon reloading manual or Alliant reloading manual. They are available where you buy powder and shot.

See this previous discussion on Dram equivalents:

Shotgunworld

Basically it as an older form of measurement that is still being used, however most reloading manuals use it as a reference where the recipe uses a 3 dram load with grains of powder being the actual weight and the dram a reference to the "power" of a load. Given that a max dram load is a heavy or magnum load.

"i guess i am getting confused on how the different shot sizes affect each shot or if the ballistics says velocity can be the same with different shots"
This is confusing to me?? shot sizes related to the actual size of the pellets, like 7.5 or 8 or the weight of the shot drop 1oz or 1.25oz? You say you have an 1-1/8 charge bar, and powder bushings?

Start with what you are wanting to accomplish with your reloading...a low recoil hunting load, a high velocity pheasant load, a general trap load, what do you want to shoot ??